In many cardiac pacing, defibrillation and cardioversion applications, it has been found useful to employ an atrial "tine" on the lead, to improve positioning and fixation of the lead electrode against or in close proximity to the atrial wall. For a DDD type pacing lead, for example, where a single lead is used to pace and sense in the ventricle and the atrium, there is no distal end of the lead within the atrium which can be simply guided into a position where it can efficiently pace and sense. Rather, it is necessary to include some design feature to ensure that the lead portion carrying the atrial electrode or electrodes is held close enough to the atrial wall to provide reliable operation. It has been found that incorporation of an atrial tine, which in this context is a relatively small arm, or extension from the main lead body, can provide a marked improvement in terms of holding the atrial electrode or electrodes in good position. Examples of leads which use such atrial tines are shown in the patent art, e.g., U.S. application, Kruse et al., Ser. No. 08/794,402, filed Feb. 3, 1997. It is to be understood that the atrial tine carries one or more electrodes at its distal end, and a coil conductor or conductors for electrically connecting to such electrode(s).
Conventionally, the lead is inserted into the heart through an introducer, which is a hollow tube having in inner lumen of greater diameter than the lead body diameter. The introducer is first inserted into a vein and then down into the heart, in a well known manner. Following this, the lead is guided through the introducer into the heart, and positioned for optimum pacing and sensing. Generally, re-positioning is required, as often the first attempt does not produce the best possible position for stimulation threshold. The re-positioning involves withdrawing the lead back through the introducer, and then reinserting it, e.g., so that the far distal end is positioned in the right ventricular apex. A problem arises in such re-positioning, where the lead carries an atrial tine. When the lead is withdrawn, the atrial tine is often caused to kink within the introducer. Extending the tine longitudinally is not a problem, but transverse kinking often occurs, which produces high stresses in the electrode coil (conductor). Such kinking can be caused several times, depending on how many times the physician needs to re-position the lead. Tests have shown that this can lead to coil breakage, which would destroy the atrial function of the lead. Coil breakage in a lead is, of course, disastrous for the patient, and any condition which could accelerate such a result must be avoided.
Another problem that bothers many physicians during lead introduction is that of blood leakage through the introducer. The introducer inner diameter is necessarily larger than the lead body diameter, in order to permit easy passage through the introducer, and to accommodate, e.g., fixation type tines as may be positioned at the distal end of the lead, and which extend laterally from the lead body. For example, for a 14 French introducer and an 8 French body diameter lead, a lot of blood leakage occurs between the lead body and the introducer while the physician maneuvers the lead through the introducer and into position.
It is to be noted that generally it is not a solution to withdraw the introducer before repositioning the lead. If this is done, it is necessary to squeeze the vein around the lead body in order to reduce blood leakage. Such a procedure becomes even more difficult, if not impossible for one physician, when a stylet has to be inserted for the repositioning. In any event, if the repositioning takes a long time, there is such significant blood leakage that this is unacceptable to most physicians. Further, if the introducer is not in place during repositioning, the atrial tine may enter a vein junction or other unintended area, and thus the introducer is kept in place to protect against such a possibility.
In view of the above, it is seen that there exist several problems with the current method and apparatus for introducing leads into a patient's heart for cardiac treatment. It is desirable to provide an improvement to reliably safeguard against atrial tine transverse kinking, and also to reduce the blood leakage through the introducer at time of lead implantation. It is an object of this invention to provide a simple but effective way to both prevent transverse tine kinking and to substantially eliminate the undesirable blood leakage through the introducer.